The present invention relates to a method of joining Al-members, and more particularly to brazing of heat exchange components and to the resulting heat exchangers provided by such method. The method is suitable for production of, e.g., automotive heat exchangers, radiators, condensers, evaporators or other devices.
Brazing of aluminum articles is presently conducted either as flux brazing, applying flux and brazing (sheet) material (AlSi) introduced between the articles, or in vacuum furnaces, using an Al-Si alloy as cladding or coating layer on the surface of the to be joined articles.
A problem experienced with heat exchangers made of aluminum is pitting corrosion. Consequently, zinc coating applied as a thin surface layer, typically up to 5 .mu.m (35 g/m.sup.2) on Al-substrates followed by diffusion heat treatment, has been used in order to improve the corrosion resistance of heat exchangers. Different brazing materials, e.g. AlSi or AlZnSi, are applied on members in the form of coating layers to provide filler material prior to the brazing operation.
The drawback in common with the above brazing methods is the necessity to apply brazing material in amounts which significantly increase the weight and cost of the assemblies, e.g. by using AlSi-clad Al-finstock in heat exchangers, where the thickness of the AlSi layer is typically 10% of the total sheet thickness. During the brazing cycle, Si will diffuse into the core, thus depleting the layer of Si and thus raising the liquidus temperature. This effect complicates the brazing process and requires close temperature control.
Furthermore, the present methods are rather complicated requiring several separate steps, and an inadequate corrosion protection can be experienced with substrates having no zinc treatment prior to the joining step.